Scum is essentially a frothy substance formed in reactors during the course of any biochemical or chemical reaction and is responsible for hindering the reaction rate. The reaction even gets terminated with the accumulation of scum in the reactor. This has been a serious problem of much concern for any biotechnological and chemical industry. Treatment of wastewater and industrial effluent through biological process has attained much focus in the present day scenario. Formation of scum during the course of waste treatment poses a major challenge to the environmental scientists too.
The performance of biochemical/biotechnological process depends mainly on the organic constituents, essentially of lipid, protein and carbohydrates present in the feed material. In the case of wastes treatment, industrial and municipal solid wastes are in general mixtures of biodegradable and non-biodegradable matters and the organic matter contents in the raw feed fluctuate widely. In view of the fluctuations in the constituents of the organic matter, and variation in organic loading rates to the reactors, scum formation and foam generation are bound to take place within the digester. The scum layer formed on the surface of liquid aids foaming when the gas evolution rate is high. The accumulation of foam in the gas space inside the reactors prevents the release of gas from the liquid and also the flow of gas from the reactor to the gas collection facility. The formation of scum layer and foaming leads to increase of backpressure inside the reactor and causes discharge of scum and foamy materials through the overflow arrangement of the reactor. In this situation the reactor cannot be operated at the designed feed rate. The feeding can be resumed only after removal of foam and scum layer from the reactor. This has prompted research into providing options to carry out aforesaid reactions in scum free environment to ensure that reaction is not hindered.
Reference is made to Lingappa et al (U.S. Pat. No. 4,349,355 9, 1982), who worked on Methane generator wherein the gas collector slidably mounted in the upper portion of the generator is provided with rods that extend downward through slotted retainer into the organic material for agitating the organic material within the liquid slurry. The characteristic feature of the system is that the scum formed on the surface is only pierced by the rods and its effect is intermittent as the rate of movement of rods again depends on the rate of gas production and the rotating movement of to and fro in the slots causes piercement of scum only in the surface area covered by the slots where the rods are rotating and the remaining area is undisturbed. The major limitation associated with this arrangement is that it does not remove scum from the surface and it aids gas production only in the area where the surface is pierced and other areas the scum builds up on the surface.
Reference is made to Tamura Tadao (JP6210296, 08, 1994), who worked on scum removal device of purification tank, wherein scum removal device ejects pressurised water to remove the scum only from the wall surface of the overflow trough. The major limitation is that this device does not effectively remove the scum from the surface of liquid where the scum is generated in the purification tank, as the blowing pressurised water cannot cover the entire liquid surface area and physically break the entire scum layer for its efficient removal along with overflow water.
Reference is made to Abe Takao et al (JP2002348948, 12, 2002), who worked on a scum removal system wherein the scum removal device removes the scum in the sewerage. The major drawback is that this system is not provided with any arrangement to break the scum formed in the liquid surface or prevent the scum formation.
Reference is made to Tuomikoski Pekka (WO03045526, 06, 2003), who worked on apparatus for removal of surface scum wherein a scraper assembly pushes the surface scum or supernatant sludge in a rectangular settling tank or clarification basin. The apparatus described is designed only to scrap the scum from the surface to the discharge point. The major limitation associated with this is that this apparatus operates only to push the scum formed on the surface towards the discharge point and it does not have any arrangement to prevent scum formation on the liquid surface itself where the scum layer is formed.
Reference is made to Tuomikoski Pakka (WO03095061, 11, 2003), who worked on apparatus for the removal of surface scum in a circular processing space wherein the surface rake fitted with mechanical aerating device enhances the passage of floating scum to the outlet mechanism in a circular processing space such as settling tank or the like. The major drawback is that this apparatus does not break the scum or prevent formation of scum layer.
In hitherto known devices main drawbacks are inadequate components in the apparatus to prevent formation of scum layer leading to incomplete removal of scum from the liquid surface. In hitherto known devices attempts have been made only to enhance passage of floating scum to the discharge point but not prevention of scum layer formation.